Putting
It All TogetherThe
most trouble that I've had with the design has been designing the backup system.
There are a number of ways to heat a house. I frequently had to tell myself
to keep it simple! Let's start with the primary heating system - the solar
system. (We're not talkin' planets here, although some of these system were
world's apart.)

Primary
Heat Source: Solar
I have to be careful how I phrase this, because if I say that the solar heating
system will take care of the majority of our heating needs, it will stay cloudy
for the next 50 years. Good ol' Murphy's Law. So let's just say that more
than 50% of our heating needs should be taken care of by solar heating. Here's
the final design for the primary system:

(Click
on the image to see a larger view.)

Although
a water storage tank would give me greater control and greater heat storage
efficiencies, the sand bed approach is simpler with no maintenance required.
A water tank would need to be cleaned every so often and might eventually
leak. No maintenance is a wonderful thing. Plus, the system can run itself.
A DC pump will only circulate the heating fluid when the sun is available
to heat the solar hot water collectors. It's simple and it's a proven design.

During
the non-heating season, the majority of the solar collectors will be covered
to keep the system from overheating, yet allow enough heat through to heat
the domestic hot water. (This is one of the advantages to locating the panels
at ground level.)

Auxiliary
Heat Source: Wood Stove / Backup BoilerKeep it simple. I have to keep telling myself this.
I really wanted to heat water with some sort of a stove, but the more I thought
about it, the more I shied away from the idea. The best way to burn wood is
a full burn -- meaning that all the gases are burned. Temperatures need to
approach 1,200F in order for a full burn, and newer, non-catalytic stoves
can achieve this. This achieves a number of benefits. The wood burns very
efficiently producing hardly any creosote at all and it beats the EPA's clean-air
standards. It's good for the environment and gets more BTUs out of the wood
and into your house.

Most
wood boilers do not burn the wood completely and those that claim that they
do have not passed the EPA's standards. The key is to getting the most BTUs
out of the wood and a wood burning stove does the best job.

In
the event that we are not home for an extended period, a backup boiler will
kick in to keep the house at a relatively warm level if it's a cloudy day.
We may also add a small space heater to heat both bathrooms if needed.

Domestic
Hot WaterAnother piece to the puzzle that I have neglected to mention so
far is domestic hot water. An eighty gallon storage tank will be heated via
the solar collectors using a heat exchanger. Water heated in the tank will
then flow to an Aquastar on-demand (solar version) hot water heater. The heater
is quite unique. The heater will vary it's BTU output based on the temperature
of the incoming water. It is quite efficient and should work beautifully.
If the temperature of the water is hot enough, (on a sunny day) the heater
will not turn on at all and if the temperature of the water is luke warm,
it will heat it up just enough to the proper level.